CS31C - Concurrent Session 31C: Rapid Overtopping Evaluation for State-Regulated Dams in North Carolina

Research Triangle Institute International (RTI) along with the State of North Carolina developed an efficient method to assess dam risk at large scale to prioritize rehabilitation and regulation updates. Dam failures significantly exacerbate impacts to downstream communities during flood events, and it was not well understood which dams across North Carolina were at risk of overtopping. Hurricane Matthew (2016) and Hurricane Florence (2018) caused massive flood damage in the Neuse, Lumber and Cape Fear River basins in North Carolina. In response, the state launched multiple flood control initiatives, including a study for the Cape Fear basin in which RTI evaluated the potential of overtopping for 261 dams.

Pertinent characteristics for each dam such as reservoir volume, embankment elevation, spillway type and dimensions were collected for all dams by RTI partners. RTI developed an automated tool which utilized survey data to calculate the elevation-discharge relationship for each dam. Hydrologic models were then produced and executed for each dam, using automated tools, to determine which dams are most likely to overtop for the 36 design storm conditions. The process automation allowed for the nearly 10,000 required model runs to be performed under a tight timeframe and for a reasonable budget.

Results of this overtopping analysis are used by the state to prioritize and monitor dams before, during, and after extreme rainfall events. The state has also incorporated the data from the overtopping studies into the Natural Resources Conservation Service’s DamWatch tool, which allows officials to produce an alert when a threshold is reached at a particular dam. Based on the forecast data and overtopping risk, the state can provide guidance to dam owners ahead of an extreme precipitation event such as a hurricane. RTI’s dam assessment study was part of a larger NCDEQ effort that received the Southeast Regional Award from the Association of Dam Safety Officials as well as an innovation award from the NC Department of Environmental Quality.